Technical Field
The present invention relates to a plurality of DC/DC converters, a switching power supply device including a plurality of DC/DC converters, and an electronic apparatus using the switching power supply device.
Description of the Related Art
With an increase in performance and functionality of mobile devices, a reduction in size and an increase in power capacity of the mobile devices are required. In order to meet the requirements, a DC/DC converter which is provided in the mobile devices needs to have a smaller size, high power capacity, and high efficiency.
In view of the above, a multi-phase power supply technique is known in which a plurality of DC/DC converters are connected in parallel to each other. The converts each have a conversion (switching) time that is shifted at equal intervals to output values that are cancelled out to reduce ripple, thus reducing the size of a passive element forming a filter, which is required for output.
Further, heat can be distributed over the DC/DC converters, such that radiation performance required for each DC/DC converter is lowered, thus reducing the size of the device. When a small load (various circuit units that consume a small amount of current) is driven, some DC/DC converters are stopped. This improves entire power conversion efficiency and maintains high efficiency in a wide load range from a light load to a heavy load.
The multi-phase switching power supply device may be implemented using a control unit and a plurality of driving units. While the state of the driving waveform phase of each driving unit which is output from the control unit can be appropriately changed to perform a multi-phase operation, it is difficult to reduce the size of the device by the mounting area of the control unit. Alternatively, the multi-phase power supply device may be implemented using only a plurality of driving units, without using a control unit. Since the control unit is not required, the size of the device is reduced by a space corresponding to the unnecessary control unit.
The multi-phase switching power supply device without a control unit does not have a particular problem when the number of operation phases is fixed, but needs to have a stable and appropriate operation phase switching unit when the number of operation phases is switched.